Dearomative spiroannulation of indoles enabled by the diaza-[1,2]-Wittig rearrangement

The first diaza-[1,2]-Wittig rearrangement-enabled dearomative spiroannulation (DSA) reaction of indoles is reported. In contrast to the previous dearomatization approaches using C3-functionalized indoles, metal catalysis, and/or external oxidants, this DSA protocol can convert readily available C3-unfunctionalized indoles into biologically and synthetically important spiroindolenines via a metal-free and redox-neutral process. A mechanism study demonstrates that the reaction process involves a three-component reaction of indoles, triazolediones, and anhydrides/acyl chlorides via the sequence of C3-amination, the diaza-[1,2]-Wittig rearrangement to break the N-N bond and the aromaticity of the indole, and intramolecular cyclization to form spiroindolenines. Notably, its asymmetric version has been accomplished to prepare various enantio-enriched spiroindolenines bearing a C-N axis and a spiro-center. Reported herein is the first diaza-[1,2]-Wittig rearrangement-enabled dearomative spiroannulation reaction of indoles. This protocol features metal-free conditions, a redox-neutral process, a broad substrate scope, and a good yield.